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Weather Hazards and climate change - Coggle Diagram
Weather Hazards and climate change
Weather hazard
Is a natural hazard caused by changes in the Earth's atmosphere.
Structure of the atmosphere
The atmosphere consists of 4 layers: the troposphere, stratosphere, mesosphere and thermosphere.
The troposphere is the lowest layer of the atmosphere. This is the layer were we live and where weather happens.
The boundary between the stratosphere and the troposphere is called the tropopause.
The height of the tropopause varies with location, being higher over warmer areas (up to 15km) and lower over colder areas (around 10km).
The earth is a sphere, which means that the sun's energy its the equator more directly than the poles.
As the air at the equator is heated, it expands, rises and tends to move towards the poles. This displaces colder air, causing large scale atmospheric circulation and creates an ever-changing areas of high and low pressure we are familiar with in our every day weather.
Heat energy is transferred through the circulation of cells and ocean currents.
Pressure
Sinking air forms areas of high pressure. Surface winds move outwards from these areas.
Rising air from low pressure. Surface winds move towards these areas of low pressure.
Surface winds are distorted by the earth's rotation - known as the Coriolis effect.
The patterns of pressure belts and winds are effected by seasonal migration of the thermal equator.
Cells
Hadley cells stretch from the equator to latitude 30 degrees north and 30 degrees south.
Warm trade winds blow towards the equator. At the equator, the trade winds from each hemisphere meet. The warm air rises rapidly causing thunderstorms. An area of low pressure is formed in the Inter Tropical Convergence Zone (ITCZ), where air from two cells meets over the equators. The air at the top of the troposphere moves towards 30 degrees north and south where it becomes cooler and starts to sink back to the earth's surface. As it descends it warms up and any moisture is evaporated. Thus creates high pressure areas with cloudless skies. The world's hot deserts are found in these areas such as the Sahara in North Africa.
Ferrel Cells stretch from latitudes 60 degrees north and 60 degrees south.
Air on the surface is pulled towards the poles. This forms the warm south-westerly winds in the northern hemisphere and the north-westerly winds in the southern hemisphere. These winds collect moisture as they blow over oceans on the Earth's surface. At about 60 degrees north and 60 degrees south, they meet cold air from the poles. The warm air rises over the cold air as it is less dense. This produces low pressure at the earth's surface pressure systems known as depressions. Some of the air returns to the tropics and some is diverted to the poles as part of the polar cells. The cell has a motion to the right in the northern hemisphere and to the left in the southern hemisphere. This is called the Coriolis effect.
Polar cells stretch from latitudes 60 degrees north and south to the north and south poles.
The air sinks over the poles producing high pressure. The air then flows towards the low pressure in the mid latitudes about 60 degrees north and south. Here it meets the warm air of the ferrel cells.
Jet streams
In the upper atmosphere, wind blows around the earth in a westerly direction. Within these winds, there are bands of extremely fast moving air known as jet streams. The jet streams can be found in two areas of the world
Polar jet streams - This is formed when cold polar air meets warm tropical air high above the Atlantic ocean. This normally occurs between latitudes 40 degrees and 60 degrees north and 40 and 60 degrees south. This occurs at the division between polar and Ferrel cells
The subtropical Jetstream - This is also generally in a westerly direction. It can be found at approximately 25 degrees north and 35 degrees south.
Causes of climate change
Natural
Milankovitch cycles.
Human
Milankovitch cycles
Milankovitch cycles refers to how the Earth's orbit changes around the sun and how this impacts on the solar radiation the Earth receives. When the Earth receives less solar radiation, colder temperatures result and this can lead to a glacial cycles.
Eccentricity
The Earth encounters more variation in the energy that it receives from the sun when the Earth's orbit is elongated than it does when the Earth's orbit is more circular.
The path of the Earth's orbit is altered from a circle to an ellipse. This cycle takes around 100,00 years
Tilt
The tilt of the Earth's axis varies between 22.2 degrees and 24.5 degrees. The greater the tilt angle, the more solar energy the poles receive
Axial tilt is also known as obliquity. The earth spins on its own axis. The axis changes from 22.1 degrees to 24.5 degrees. It takes 41,000 years for the earth's axis to change from 22.1 to 24.5 and back again
Precession
A gradual change, or "wobble", in the orientation of the Earth's axis affects the relationship between the Earth's tilt and eccentricity.
The Earth's axis wobbles like a spinning top. One full cycle takes around 26,000 years. The Earth's axis wobble is caused by the gravitational action of the sun and the moon.